Note: The risk of bias by domain corresponds to the highest risk of bias among outcomes by domain.
The overall risk of bias corresponds to the overall highest risk of bias assessed among outcomes.
| Bias | Author's judgement | Support for judgement |
| Randomization |
Low |
Quote: "patients were block-randomized in a 1:1 ratio based on the presence or absence of peripheral B-cells using a computerized algorithm (Randomizer)... Blinding of vaccines was ensured by the Central Pharmacy of the Vienna General Hospital, where dose aliquots were prearranged in syringes without reference to the vaccine type used."
Comment: Allocation sequence random. Allocation sequence probably concealed. |
| Deviations from intervention |
Low |
Quote: "laboratory assessors and patients were blinded".
Comment: Blinded study (participants and personnel/carers). Hence, deviations did not arise because of the trial context. Analysis on those who received at least one dose of the intervention. As we are assessing the effect of assignment to intervention, the analysis method performed on these safety outcomes, was considered appropriate. Risk assessed to be low for the outcomes: nAb Seroconversion rate, Mortality, Local adverse events, and Systemic adverse events. |
| Missing outcome data |
Some concerns |
Comment: 51 participants randomized; 46 participants analyzed.
Data not available for nearly all participants randomized. No evidence that the result is not biased. Reasons: 2 vs 3 participants withdrew consent between the screening and the baseline visit before booster. Missingness could depend on the true value of the outcome. Missingness is not likely to depend on the true value of the outcome due to balance between arms. Risk assessed to be low for the outcomes:nAb Seroconv rate, Mortality, Local adverse events, and Systemic adverse events. |
| Measurement of the outcome |
Low |
Comment: Method of measuring the outcome probably appropriate.
Measurement or ascertainment of outcome probably does not differ between groups. Blinded study (outcome assessor). Risk assessed to be low for the outcomes:nAb Seroconv rate, Mortality, Local adverse events, and Systemic adverse events. |
| Selection of the reported results |
Low |
Comment: The protocol, statistical analysis plan, and registry were available (registry dated May 19, 2021).
Outcome pre-specified. Results were not selected from multiple outcome measurements or analyses of the data. Trial analyzed as pre-specified. Risk assessed to be low for the outcomes:nAb Seroconv rate, Mortality, Local adverse events, and Systemic adverse events. |
| Overall risk of bias |
Low |